def setup
  background(220)

  v1 = createVector(3, 4, 5)
  v2 = createVector(2, 3, 4)
  v3 = P5Vector.sub(v1, v2)

  div = createDiv("v3: [#{v3.x}, #{v3.y}, #{v3.z}]")
  div.position(10, 10)
  div.style('font-size', '14px')
  div.style('width', '100px')
end

# red vector - blue vector = purple vector
def draw
  background(240)

  v0 = createVector(0, 0)
  v1 = createVector(70, 50)
  drawArrow(v0, v1, 'red')

  v2 = createVector(mouseX, mouseY)
  drawArrow(v0, v2, 'blue')

  v3 = P5Vector.sub(v1, v2)
  drawArrow(v2, v3, 'purple')
end

# draw an arrow for a vector at a given base position
def drawArrow(base, vec, myColor)
  push do
    stroke(myColor)
    strokeWeight(3)
    fill(myColor)
    translate(base.x, base.y)
    line(0, 0, vec.x, vec.y)
    rotate(vec.heading)
    arrowSize = 7
    translate(vec.mag() - arrowSize, 0)
    triangle(0, arrowSize / 2, 0, -arrowSize / 2, arrowSize, 0)
  end
end